This application is based on applications No. 11-35692 and No. 11-293849 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a light measuring apparatus and a calorimeter for measuring the spectral characteristics of pulse-like visible light, infrared light, or ultraviolet light, which are used in an illuminometer, an IR spectrophotometer, a UV spectrophotometer, an optical power meter, a luminancemeter, a photometer or the like.
2. Description of the Related Art
There has conventionally been known a calorimeter as shown in FIG. 8. The calorimeter measures reflected light from a sample 101 under measurement when it is illuminated with a pulse beam outputted from a lamp 110. The reflected light from the sample 101 under measurement is branched to be transmitted by filters 120R, 120G, and 120B having different spectral sensitivities, received by photoelectric converting elements 130R, 130G, and 130B, such as photodiodes, and converted to current signals responsive to received light intensities. The current signals are converted to voltage signals by current-to-voltage converting circuits 140R, 140G, and 140B.
The voltage signals are charged and integrated in respective integrating circuits 150R, 150G, and 150B for a specified time and held as integral signals. The integral signals held are selected in turn by a multiplexer 161 and converted to digital values by an A/D converter 162 such that their signal levels are detected by a CPU 163.
When the sample under measurement is illuminated with the pulse beam from illuminating means in the calorimeter, it is difficult to completely block light other than the beam from the illuminating means. Accordingly, the light for illuminating the sample under measurement includes fixed light other than the pulse beam and offset. To remove the influence of such factors, there has been known a method of obtaining measurement data derived only from the pulse beam from the illuminating means and free from the influence of fixed light and offset by subtracting an output value of the A/D converter 162 resulting from the integral signal indicative of integration for the specified time, during which the pulse signal is not outputted from the illuminating means, from an output value of the A/D converter 162 resulting from the integral signal indicative of integration for the specified time including the time during which the pulse beam is outputted.
However, the conventional colorimeter shown in FIG. 8 requires one integrating circuit for one photoelectric converting element. If the number of photoelectric converting elements is increased to provide particular spectral characteristics, therefore, the number of integrating circuits is increased accordingly and the area occupied by the integrating circuits is also increased. This leads to the problem that a circuit board on which circuit components shown in FIG. 8 are mounted is increased in size.
To provide high-accuracy measurement data free from the influence of fixed light and offset by following the procedure described above, it is necessary to repeatedly perform, to the integrating circuit, operational control such as integration of the inputted voltage signal, retention of the obtained integral signal, and complete discharging of the integral signal, which causes the problem that complicated control should be performed with respect to the integrating circuit.
There has also been known a method of improving measurement accuracy in a conventional circuit as shown in FIG. 8, in which a signal level is held at a proper value by switching, during the charging of the integrating circuit, the capacitance of the capacitor of the integrating circuit or increasing or reducing a charging time based on variations in charging voltage within a specified time. However, the method also has the problem that complicated control should be performed with respect to the integrating circuit.
It is therefore an object of the present invention aiming at solving the foregoing problems to provide a light measuring apparatus and a colorimeter that can be reduced in size and price by obviating the necessity to provide an integrating circuit for pulse-like measuring light.
Another object of the present invention is to provide a light measuring apparatus and a calorimeter capable of performing high-accuracy measurement even in the case of obviating the necessity to provide an integrating circuit for pulse-like measuring light.
To attain the above objects, a light measuring apparatus in accordance with a first aspect of the present invention comprises: n (n is an integer equal to or more than 2) photoelectric converting elements for receiving pulse-like measuring light and outputting electric signals responsive to received light intensities; n time constant converting circuits provided to correspond to the n photoelectric converting elements, the time constant converting circuits outputting elongated electric signal obtained by elongating the electric signals outputted from the corresponding photoelectric converting elements in the direction of a time axis; a signal level detector for detecting the levels of the elongated electric signals at different times in the direction of the time axis; and an calculator for calculating respective integral values of the n elongated electric signals by using the result of detection from the signal level detector.
A light measuring apparatus in accordance with a second aspect of the present invention comprises: n (n is an integer equal to or more than 2) photoelectric converting elements for receiving pulse-like measuring light and outputting electric signals responsive to measured light intensities; n time constant converting circuits provided to correspond to the n photoelectric converting means, the time constant converting circuits outputting elongated electric signals obtained by elongating the electric signals outputted from the photoelectric converting elements in the direction of a time axis; a signal amplifier having m (m is an integer equal to or more than 2) selectable amplification factors, the signal amplifier outputting n amplified elongated electric signals obtained by amplifying each of the elongated electric signals with the selected one of the amplification factors; a signal level detector for detecting the levels of the amplified elongated electric signal at different times in the direction of the time axis; amplification factor setting means for setting a proper amplification factor selected from the m amplification factors based on the result of detection from the signal level detector; and a calculator for calculating respective integral values of the n amplified elongated electric signals by using the result of detection from the signal level detector.
A light measuring apparatus in accordance with a third aspect of the present invention comprises: a first photoelectric converting element for receiving pulse-like measuring light and outputting a first electric signal; a second photoelectric converting element for receiving the pulse-like measuring light and outputting a second electric signal; a first time constant converting circuit provided to correspond to the first photoelectric converting element, the first time constant converting circuit outputting a first elongated electric signal obtained by elongating the first electric signal in the direction of a time axis; a second time constant converting circuit provided to correspond to the second photoelectric converting element, the second time constant converting circuit outputting a second elongated electric signal obtained by elongating the second electric signal in the direction of the time axis; and a calculation controller for sampling, a plurality of times, each of the first and second elongated electric signals at given time intervals and calculating respective integral values of the first and second elongated electric signals by using plural sets of sampling data.
In an embodiment, a colorimeter having the light measuring apparatus in accordance with the first, second, or third aspect is shown by way of example. The calorimeter comprises: an illumination lamp for outputting a pulse beam for the illumination of a sample under measurement; and an optical member for dividing a light beam from the sample under measurement into n light beams having-different characteristics. The pulse beam outputted from the sample under measurement when the sample under measurement is illuminated with the pulse beam from the illuminating lamp is divided into n beams such that the beams having different spectral characteristics are received as measuring light by the corresponding photometric converting elements.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.